1. Field of the Invention
The present invention relates to surgical reamers that create bone cavities; and, more particularly, to a flexible disposable reamer shaft that may be attached to a modular disposable spherical or tapered hollow reamer, the disposable reamer shaft being concentrically attached to a modular hollow reamer to provide wobble-free rotation of the reamer tool.
2. Description of the Prior Art
Reaming of the internal canal of bones is required in many surgical procedures of orthopedic surgery. These procedures include hip replacement and shoulder replacement, and the like. Reamers are used in procedures that involve creation of acetabular bone cavities that accept a properly sized acetabular cups. Surgical reamers are used in orthopedic surgery to enlarge medullary canals of long bones such as the femur and humerus in preparation for insertion of fixation devices, performing an intramedullary osteotomy, stimulating bone growth. The medullary canals of bones are seldom straight. More typically, the canal will have some degree of curvature to it. Should a straight and rigid series of reamers be employed to enlarge the canal, there is considerable likelihood that the reamer, if not being capable of following the bone's curvature, will jam or will not remove the desired uniform amount of bone tissue. In such a situation excessive tissue removal occurs in at least one plane as a reamer advances. For this reason, medullary canals are almost always prepared with reamers having a flexible shaft. Generally reamers for use with a flexible shaft utilize a central bore through both the reamer and drive shaft. The central bore is intended to receive a long, small diameter guide pin, which is initially inserted into the medullary canal to act as a track for the advancing reamer. However, the use of a flexible shaft does not always solve the problem of excessive tissue removal and jamming. When this jamming occurs with the prior art cutting head, the long guide pin has to be withdrawn from its position to assist in dislodging the reamer cutting head. This can result in a loss of reduction at the fracture site. Heretofore, the shape of the reamer cutting heads has been basically a cylinder with a short angled area towards the front that would do the cutting and another short angled area at the back of the head that is intended to facilitate the removal of the reamer. Therefore, the flexible reamer shaft has to connect to a tapered hollow reamer or a spherical reamer without wobble, maintaining local predictable concentricity as the surgeon adjusts the reaming process.
U.S. Pat. No. 3,554,192 to Isberner discloses a medullary space drill. The medullary space drill includes a flexible shaft carrying at its opposite ends respectively a drill head, and an adapter piece adapted to be connected for rotation with a driving means. The shaft comprises a plurality of parallel flexible elements arranged to provide a central passage for receiving an elongated guide element. The medullary space drill disclosed by the '192 patent has a flexible shaft portion made from a plurality of circular rod or wire elements arranged in a circular fashion, forming a central hole for accommodating a guide pin. The bundle of rods or wires at the ends is jointed by welding or brazing, preserving the circular arrangement. When torsion is carried by the bundle of rods, there is a twist between the driven end and the reamer drilling end; the magnitude of the twist is a function of reaming torque needed. Thus, the twist may be irregular especially when the bone has hard and soft locations, thus delivering an unsteady torque. Also flexure of the flexible shaft portion requires some of the wire or rod elements of the bundle to move outward or inward and a single wire or rod may pop out of the circular arrangement if the flexure bend radius demanded is sharp. Even though the patent states that the flexible shaft is easy to clean, the bone fragments will dislodge and enter the central hole. Since the '192 patent contemplates cleaning of the flexible shaft, it is clearly not a disposable flexible shaft.
U.S. Pat. No. 4,362,520 to Perry, discloses a flexible enclosed shaft. This heavy-duty flexible shaft accommodates for misalignments between an input and output shaft. The flexible shaft is comprised of a multiplicity of hollow, individually fabricated, interfitting members housed in a tubular, bendable shaft. Each segment is intimately engaged, one within the other, yet the segments are so designed to allow for limited longitudinal movement while restricting circumferential movement between segments during torsion transmissions from the input to the output shafts. The flexible enclosed shaft disclosed by the '520 patent is a shaft designed for industrial use, but is not for medical use since it requires lubrication. The torque is delivered from the input shaft to the output shaft through the interfitting members. The cylindrical pipe merely serves to contain the interfitting members and does not carry any toque. The shaft does not accommodate a guide pin.
U.S. Pat. No. 4,541,423 to Barber discloses drilling a curved hole in bone tissue. This drilling apparatus is for attachment to a rotary motor that includes a flexible shaft confined in an elongated tubular sheath. The sheath is formed from a semi-rigid material which is bendable to a desired curvature, at the use site to select the curvature of the drilled hole, and which is rigid enough to retain that curvature in use. A drilling bit is fixed to one end of the flexible shaft, and includes a shank coacting with the distal end of the sheath to rotationally guide the drilling bit. The flexible shaft projects from the sheath at the proximal end so that both components may be secured to a drilling motor which is manipulated to guide the sheath while rotating the cutting bit. The sheath may remain in the drilled hole temporarily as a liner to guide the passage there through of a relatively stiff wire or other filamentary member. The sheath does not rotate and deliver the torque. Rather the spring-like flexible shaft resides inside the sheath and delivers the torque to the drill bit. The flexible shaft within the sheath is not indicated to accommodate a guide pin. Thus the drill bit and the reaming location is only controlled by the tip of the sheath, which is distal from the reaming location in the bone canal.
U.S. Pat. No. 4,706,659 to Matthews, et al. discloses a flexible connecting shaft for an intramedullary reamer. The flexible connecting shaft for an intramedullary reamer has several short segments or links are attached together to form an elongated flexible shaft. The shaft is designed to bend along its longitudinal axis while transmitting torque without any lag in such transmission, due to the specific attachment means for the links. A link at one end of the flexible shaft as made by a plurality of the links includes means provided for attachment to a torque providing device such as an electric motor. At the opposite end of the shaft, the last link includes structure thereon enabling connection to a drill bit. The plurality of short segments or links made of a material such as stainless steel, chrome cobalt-molybdenum alloy, titanium, or other metals. Each segment or link includes a male end and female end with each male end being specifically configured so as to interengage with the female end of an adjacent link. The links may be connected together to form a reamer shaft by inserting through the aligned holes in the individual links a flexible rod. This rod will hold the links together while allowing the flexing of the shaft about the longitudinal axis. The reamer shaft which will flex, curve or bend while transmitting torque and while at the same time reaming naturally curved long bones without cutting through the cortex or side wall of the bones. The links are only flexible at the joint locations and the inserted flexible shaft suffers piece wise bending, especially when the segment lengths are large. The flexing of the shaft requires free space between the links and as a result the torque transmission is not smooth in spite that the patent states that it is free lag in torque transmission. The flexible rod inserted does not function as a guide pin that guides the reamed bone cavity. The drill or reamer is not indicated to accommodate a guide pin and therefore the drilling or reaming location within a bone cavity can wander when the flexible shaft is flexed by the surgeon.
U.S. Pat. No. 4,751,922 and EP 0253526 to DiPietropolo disclose a flexible medullary reamer. The flexible medullary reamer is designed for shaping the medullary space of bones. The shaft is comprised of a single solid element. The flexible medullary rotational reamer for clearing, enlarging or otherwise modifying the medullary space of bones has a flexible shaft with a cutting head at one end and an adaptor piece at its opposite end for connecting said shaft to a rotational drive element, thereby causing rotation of the shaft. The shaft has a small diameter axial bore throughout its length to receive an elongated guide element. The flexible reamer shaft is a carbon fiber reinforced composite adapted for transmitting the torque from the drive mechanism to the drilling element while being still flexible. The torque transmission element has the high modulus carbon fibers embedded in low modulus polymer. Creating the composite and modulus mismatch does not provide smooth flexibility or torque transmission of the flexible shaft since the carbon fiber may delaminate from the surrounding polymer.
U.S. Pat. No. 5,122,134 to Borzone, et al. discloses a surgical reamer. The surgical reamer of the '134 patent uses a small flexible shaft to guide a reamer in an inclined orientation to enlarge a bone cavity. The reamer is guided by a guide pin. The flexible shaft in the drawing appears to be a shaft with spiral cuts. This type of shaft is expensive to make and hence is not commonly discarded after each operation and is subject to cross contamination since the flexible shaft with a central hole for a guide pin is not easy to clean.
U.S. Pat. No. 5,488,761 to Leone discloses a flexible shaft and method for manufacturing same. A shaft coupling for transmitting power includes a flexible hollow rod that extends in a longitudinal direction and has pairs of helical slots formed thereon. The flexible shaft can be rotated in both directions without jamming of the cutters. The flexible shaft of the '761 patent uses a machined helical pair or grooves to improve flexibility of the shaft. Such construction is hard and expensive to machine, and requires specialized machining techniques. The slots machined are required to be wide for effective cleaning. Due to this expensive machining process involved, the flexible shaft needs to be cleaned and reused and is not disposable. The attachment procedure for the electrical motor or the reamer head is not disclosed.
U.S. Pat. No. 5,908,423 to Kashuba, et al. discloses a flexible medullary reaming system. This apparatus for reaming a bone canal, such as the medullary canal of a femur, has a flexible shaft with a proximal end for engaging a rotary transmission source. The proximal end of a first reamer is coupled to the distal end of the flexible shaft to prepare the distal portion of the canal. The flexible medullary reaming system disclosed by the '423 patent comprises a flexible shaft to which a group of three reamers, first, second and third are attached. The first reamer reams the proximal portion of the bone canal; the second reamer reams the intermediate portion, while the third reamer reams the distal portion of the bone canal. The third reamer may be driven independent of the first two reamers. The flexible shaft is flexed from a straight configuration to position the third reamer to ream in an arc in a proximal portion of a bone. The apparatus further comprises a metaphyseal template having the shape of the prosthesis for guiding the reaming apparatus in forming the calcar region of the canal. The curvature of the medullary canal, as formed, rather than the angles formed according to the prior art, allows the implant shape to more closely match the curvature of the anatomy. This flexible shaft is of any design including a spirally wound shaft and is not indicated to be disposable.
U.S. Pat. No. 6,053,922 to Krause, et al. discloses a flexible shaft. This improved flexible shaft is used in the reaming of the medullary space in bones. The shaft is comprised of a solid element with a longitudinal bore the entire length and an appropriately formed slot which extends spirally around the shaft either continuously or segmentally. Attached to the shaft's opposite ends respectively, are a cutting head and a means of connecting the shaft to a driving mechanism. The flexible shaft of the '922 patent uses a spiral grooved solid shaft that can flex due to the interlocking segments that flex and transmit torque. The shaft has a central bore suited for a guide wire. Bone debris can easily get into the interlocking locations creating jamming of the flexible shaft. The process of making spiral grooves is expensive and the flexible shaft is not indicated to be disposable.
Foreign Patent Application Patent No. WO/2003/039378 to White discloses a drive shaft coupling and flexible surgical reamer. The reamer employs a fitting with a radially flexible member, e.g., a split collet or a super-elastic collar that receives an elongated tubular shaft of super-elastic alloy. A compression sleeve is applied to the collet, in one embodiment, while the collar is located within a counter-bore of the fitting in another embodiment. Relative motion between the shaft, fitting and collet (or collar) induces a super-elastic activation in the shaft to form the desired coupling. The drive shaft coupling and flexible surgical reamer of the '378 patent uses a super-elastic shaft made from nickel titanium alloy, Nitinol, which is a shape memory alloy. This Nitinol flexible shaft is expensive. It requires specialized heat treatment to provide shape memory properties, and thus is not disposable.
Non-Patent Document Flexible Reamers and Reaming Heads at www.chrispqld.com/easi_sterilise/flex_reamer.pdf discloses photographs of a flexible reamer. The shaft has a continuous helical groove, which enables flexible bending and torque transmission. The ends of the shaft are attached to a driving mechanism at one end and a cannulated reamer at the other end. The flexible shaft of the Flexible Reamers and Reaming Heads document uses a helical cut grooved solid shaft that can flex only at small flexure radius. Repeated flexing is indicated to result in loss of the reamer shaft shape. Bone fragments can get in between the helical cut portions, making the reamer very difficult to clean. The helical grooving is expensive; and therefore cleaning is anticipated. The flexible reamer shaft is therefore not disposable.
Non-Patent Document NT Flexible Reamer Shaft for Orthopaedic Application at http://www.fitec.co.jp/ftm/english/nt-e/reamer.htm discloses a flexible reamer shaft made from a shape memory alloy. When the shaft tube is bent, it returns back to its original shape. The ends of the shaft are attached to a driving mechanism at one end and a cannulated reamer at the other end. The flexible shaft of the NT Flexible Reamer Shaft document uses shaft metal alloy tube which can be flexed but returns to its original shape. The flexible shaft carries torque from the drive to the drill. This NT flexible shaft is expensive. It requires specialized heat treatment to provide shape memory properties, and thus is not disposable.
There remains a need in the art for a low-cost, disposable shaft that is capable of transmitting torque from the driving mechanism to a bone reamer. The disposable shaft must be flexible and enable reaming or cleaning of curved segments of a bone cavity without damaging bone tissue. The disposable nature of the low-cost flexible reamer will prevent cross contamination of bone debris, blood and tissue residues from patient to patient since cleaning of non-disposable flexible reamer shafts is usually difficult and unreliable.